What is the fluid portion of blood called?

The fluid portion of blood is known as plasma. Plasma is a yellowish liquid that makes up about 55% of total blood volume. It serves several critical functions, including transporting water, electrolytes, nutrients, hormones, and waste products throughout the body. Plasma also contains proteins such as albumin, globulins, and fibrinogen, which play important roles in maintaining osmotic balance, immune responses, and blood clotting.

Serum is often confused with plasma; however, serum is the fluid that remains after blood has clotted, and it lacks certain clotting factors. Hemoglobin is a protein found within red blood cells that carries oxygen, while platelets are cell fragments involved in blood clotting. Understanding the specific role of plasma helps clarify the overall function of blood in circulation and bodily processes.